To give you heads up Winchester model 12 never produced a imp/mod barrel
Yes, Winchester did offer IMP-MOD choked and marked guns in 12, 16 and 20 Gauge, along with CYL, WS-1, IMP-CYL, WS-2, MOD and FULL.
WS1 and WS2 weren't offered until 1934. IC, IM were offered starting around 1935-1936. CYL, MOD and FULL were offered starting in 1912.
Get you a copy of the George Madis book, The Winchester Model 12. It is the best Model 12 Book available and reflects cataloged Winchester offered options of the Model 12.
I already have a 1940's era 20 Gauge 28" FULL SR Field/Standard Grade in 98% original unmolested condition. Appreciate the offer.